Fine patterns used in the fabrication of semiconductor circuit devices and display devices, such as LCDs and PDPs, are formed by photolithography using photoresists. Photolithography has an advantage in that desired patterns can be precisely obtained, but is disadvantageous in that a number of processing steps are involved, many kinds of materials are used to maximize the effects of photoresists and large amounts of photoresists are consumed during processing (e.g., coating).
In an effort to overcome these disadvantages of photolithography, patterning for the formation of fine patterns by roll printing or inkjet printing has been proposed as a next-generation technique.
Photoresists for use in photolithography can be largely divided into positive and negative types. Of these, negative-type photoresists are photopolymerizable photosensitive resin compositions and are currently used in various applications, including photosensitizers for the formation of black matrix (BM), red, blue and green patterns, which are constituent elements of color filters for display devices, overcoat photosensitizers, column spacers, insulating materials with light-shielding properties, etc.
Heat-curable resin compositions as well as negative-type photopolymerizable photosensitive resin compositions for use in photolithography may also be used as ink compositions for use in roll printing or inkjet printing.
However, the use of photopolymerizable photosensitive resin compositions in roll printing or inkjet printing necessitates additional exposure systems other than printing equipment, which disadvantageously incurs considerable costs in the purchase and operation of the systems and requires additional processing time for exposure. Under these circumstances, techniques associated with the use of heat-curable resin compositions in roll printing or inkjet printing are used in preference to techniques associated with the use of photopolymerizable photosensitive resin compositions.
General heat-curable resins that can be used for the formation of coating films are melamine-formaldehyde, polyester, polyurethane, epoxy, phenolic, acrylic, alkyd resins, and mixtures and copolymers thereof.
A heat-curable resin used in a color ink composition for the formation of a BM, red, green or blue pattern must be highly resistant to heat and stable during storage in a mixture with a pigment and a dispersant. In view of the above requirements, an acrylic resin is the most suitable heat-curable resin.
A typical acrylic resin is prepared by random copolymerization of corresponding monomers in a mixed state in the presence of a thermal polymerization initiator. In recent years, an attempt has been made to crosslink an acrylic resin having acid groups with an ethylenically unsaturated compound in order to introduce polymerizable functional groups into side chains of the acrylic resin.
However, since the polymerizable functional groups are introduced into the acid groups of the acrylic resin, an increase in the proportion of the polymerizable functional groups in the acrylic resin implies a relatively low proportion of the acid groups left. Therefore, in the case where the acrylic resin is utilized as a negative-type photosensitive resin, the proportion of the alkali-soluble component is lowered, resulting in poor developability. Furthermore, since the acrylic resin is prepared by random free-radical polymerization of monomer having an acid group in the presence of a thermal polymerization initiator, the monomer molecules are randomly distributed in the resin to allow ethylenically unsaturated groups, which are introduced into the resin through the reaction of the ethylenically unsaturated compound and the acid groups, to be randomly distributed in the resin, leading to poor resistance of the resin to heat and chemicals.
Thus, there is an urgent need for an ink composition with excellent heat resistance, storage stability and chemical resistance.